Mechanism of cell fate choice between neural and mesodermal development during early embryogenesis

During early embryogenesis, Sox2 expression distinguishes the neural plate from other embryonic domains, suggesting that the mechanism underlying the activation of the Sox2 gene is highly relevant to the development of this tissue. At the earliest stages of neural plate development, the Sox2 enhancer N1 regulates Sox2 expression in the extending posterior end of the neural plate. The N1 enhancer is initially activated in the axial stem cells, bipotential precursors of both neural and mesodermal lineages, therefore the activation does not immediately lead to Sox2 expression. A population of axial stem cells that remains in the superficial layer starts expressing Sox2, whereas another population that migrates through the primitive streak loses the N1 activity and becomes mesoderm. Multiple signaling cascades and transcription factors, including Wnt, fibroblast growth factor (FGF), bone morphogenetic protein (BMP) and Tbx6, are responsible for the regulation of Sox2 expression in axial stem cells to guide the development of the posterior neural plate and paraxial mesoderm.